The amount of reality-bending in a science fiction or fantasy storey which the reader must absorb as a precondition of enjoying the work and appreciating the dramatic point. Science fiction has more overhead than mainstream fiction: the author is building a world that does not exist so as to stage something which cannot be illustrated in the world that does exist. Staging overhead unobtrusively but unmistakably is always a problem; the shorter the work, the harder the problem. Well-balanced storeys have no more overhead than necessary to make the dramatic point; part of the difficulty in writing sf short stories, thus, is the need to provide overhead in a cramped space. This may in part contribute to the proliferation of used furniture, which (however tacky and cliched) is at least familiar and thus requires less overhead.